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Resting energy expenditure, often called REE, is the amount of energy expended (measured as calories burned) by a person at rest. REE is important for a couple of reasons. For most people, REE accounts for about 60% of calories burned during a 24 hour period, which means the higher a person’s REE, the more calories he or she burns overall. A higher REE may help keep lost pounds from returning.
Unfortunately, REE typically drops when people lose weight. Less body mass means a person needs fewer calories to maintain the new, lower weight. A newly slimmer person must address this decreased calorie burn by exercising more, or eating less, for life. Fail to do this and the pounds inevitably, and frustratingly, return.
To study how diet composition affects resting energy expenditure, researchers randomly selected 21 obese young adults who had lost 10% to 15% of their original body weight to eat one of the following diets:
All participants followed each diet, in random order, for four weeks. The diets contained equivalent calories, and during each four-week period, researchers measured REE of each participant. Compared with their pre–weight loss REE, the decrease in REE was greatest with the high-carbohydrate diet, intermediate with the moderate carbohydrate diet, and least when participants were following the low-carbohydrate diet.
At first glance, this clearly suggests that the low-carbohydrate diet was most effective for keeping the body burning more calories after weight loss, but Dr. Jules Hirsh, a Rockefeller University obesity researcher, says not so fast. In an interview with the New York Times, Dr. Hirsh notes, “When carbohydrate levels are low in a diet and fat content is high, people lose water. That can confuse attempts to measure energy output. The usual measurement is calories per unit of lean body mass—the part of the body that is not made up of fat. When water is lost, lean body mass goes down, and so calories per unit of lean body mass go up. It’s just arithmetic. The paper did not provide information to know how the calculations were done, but this is a likely explanation for the result.”
This is one small study, and as one obesity expert highlights, we don’t yet know if the decrease in resting energy expenditure was lower on the low-carbohydrate diet, or simply appeared lower due to the loss of water weight. Still, the study suggests that diet composition influences the body, and may be a useful tool for preventing weight regain. While we wait to learn more, use our tips to find your own formula for long-term weight maintenance success.